Cranes having grapples or grab mechanisms heretofore have been used to transport massive articles such as steel or aluminum ingots at the smelter, steel mill or fabricating facilities. Typically, the grab assembly is carried by the crane and may be lowered into proper position to pick up the article between a pair of tongs. Due to the great weight of these articles, which may be many thousands of pounds, the tongs have been outfitted with tong bits or jaws to obtain positive gripping or engagement with the sides of the article within acceptable size and power requirements of the motor and drive train assemblies used to operate the tongs.
At some sites such as at soaking pits in steel manufacturing facilities, there may be a need to transport both hot and cold ingots as well as ingot molds. When hoisting a cold ingot or bloom, large or high gripping force is required to obtain a secure grip on the hard cold steel whereas a lower gripping force should be used when handling a hot ingot to reduce tong bit indentation of the relatively soft metal. Furthermore, the gripping force should be even less when handling a mold with pick-up lugs to minimize damage to the mold. Accordingly, it would be desirable and it is a principal object of this invention to provide a variable grip lifting mechanism which provides for variable, selectable gripping forces at the tong bits.